When two or more radio access networks share the same spectrum in a wireless communication system without any exclusive, dedicated and fixed sharing of spectrum, methods for spectrum allocation are needed. The spectrum allocation period can vary in length, e.g. spanning from milliseconds (i.e. dynamic allocation) to days or even months (i.e. semi-permanent allocation). The spectrum allocation method can be based on instantaneous spectrum needs, load of the radio access networks, interference tolerance of the radio access networks, bidding results from spectrum auctions, etc.
Further, spectrum allocation has to take into account the density and locations of various network nodes, such as access nodes, as well as the out-of-band characteristics of the network nodes.
Future 5G radio access networks are expected to enable new services and business opportunities leading to a large number of co-located Public Land Mobile Networks (PLMNs). Therefore, solutions for spectrum sharing and dynamic spectrum allocation are needed in future wireless communication systems. Such a need is even more stringent in densely populated areas where the need for additional spectrum is considered to be most urgent. Hence, crucial technical questions for spectrum sharing and dynamic spectrum allocation are e.g.:
How to avoid interference between co-located radio access networks?
How to share the available spectral resources in a fair and dynamic manner?
The availability of the spectrum can be inferred by using measurements and following network sharing rules agreed among all the parties involved, such as network operators, users of the adjacent bands, and spectrum authorities. The current spectrum usage can be measured not only in the temporal dimension but also in the power-density or spatial dimensions, such as locations, polarizations, and direction. The usage of the spectrum in the spatial dimension can be estimated with measurements or by using appropriate numerical analysis tools.
There are various conventional technologies related to spectrum sharing. In a Common Radio Resource Manager (CRRM), the participating radio access networks have a common entity which is governing the spectrum usage in a controlled manner. In this approach the radio access networks share information regarding their usage of the radio resources such as transmission time, power, codes, etc. A drawback of the CRRM approach is that the radio networks participating in the spectrum sharing lose their independency and may send valuable (even confidential) information of their own radio networks. With CRRM, two radio access networks are merged into a single radio access network in many aspects. This may lead to difficulties in managing the common part of the radio access network planning and operation.
Another approach is to utilize Geo-Location Databases (GLDBs) to inform of the sharing radio access networks about the free spectrum in a particular location. The GLDB should incorporate information on sharing rules determined by the local spectrum administrator. The GLDB lacks information on actual spectrum usage and local propagation conditions. The rules for the co-existence are typically very general causing inaccuracies and inefficient spectrum usage.
Cognitive Radio (CR) with in-build spectrum sensing functionalities in radio devices are suggested for detecting local white-spaces, i.e. unused spectrum. Spectrum sensing is typically implemented with power detectors, or correlators depending on the radio technology used. Spectrum sensing at the user device side may not be attractive due to the power consumption required for such a task.